The present invention relates to digital magnetic recording and reproducing apparatus using a thin film magnetic head, and more particularly to an equalized signal processing system in a peak sense type reproduced signal processing apparatus for eliminating an undershoot in a signal waveform reproduced by a thin film magnetic head.
A digital magnetic recording and reproducing apparatus using a peak sense system uses a thin film magnetic head to obtain a sharp recording magnetic field as the recording density becomes higher. However, if a thin film magnetic head is used, peaks 401, 402 (FIG. 3) of the reproduced waveform called undershoots and opposed in polarity to a main peak of the reproduced waveform appear in the vicinity of the outer edges 404 of a thin film magnetic pole 409, as shown by the broken lines 403, because the pole length is limited. When pattern data are recorded and reproduced, the undershoots interfere with the reproduced waveform in the vicinity thereof, so that the pattern peak shift increases.
Conventionally, such an undershoot is eliminated using a transversal equalizer disclosed in Japanese Patent Publication JP-A 61-59664. The equalizer creates an echo signal comprising a timewise deviated version of the input signal through a delay circuit and adds the echo signal and the input signal at a particular ratio. To level off the undershoot portion, the undershoot eliminating unit performs the following functions. The first is to delay the echo signal to the position of the undershoot portion of the input signal using the delay circuit, and the second is to add the echo signal and the input signal. A compensating signal for leveling off the undershoot is deviated to the position of the undershoot by a fixed delay element.